Refactor CI Workflow

Refactor CI Workflow

* Rename the workflow from Test to CI, since it does more than tests
* Run logtalk tests in a separate job to improve isolation
* Publish all xunit/junit test files as build artifacts to be consumed
  by a separate publishing workflow.
* Add "job summary" feature to show a formatted summary of the test
  results on the job summary status page
* Run the CI job once every Wed to ensure that there are always some
  recent builds on master that haven't expired.